A video image display apparatus to be mounted on a head, that is, a head-mounted display (hereinafter also referred to as “HMD”) has been used as a display for immersive games and the like in addition to being used as a display for remote control systems to support operation in dangerous zones in which a human cannot directly control or operation in distant places. In the case of the immersive type, a goggle-type HMD which covers around eyes and fixed on a head has been proposed, and reduction in size and weight of devices has enabled proposing lighter mobile glasses-type HMD for viewing video image content.
Meanwhile, 3D video images are increasingly popular not only as movies but also as video images of TV content or games with the spread of 3D television sets and computer displays for domestic use. The 3D video image is a video image which provides viewers with illusion of depth by providing parallax between an image provided to the right eye and an image provided to the left eye. An HMD holds a display close to the eyes of a viewer, and thus can easily present different images to right and left eyes. Therefore, the HMD is suitable to be used for viewing 3D video images.
However, since the HMD is fixed to the head portion of a viewer, when the viewer tilts the head portion, the screen tilts together with the head portion, causing a gap between a vertical axis of the screen and a vertical axis of an actual viewing zone. As such, humans sometimes get motion sickness due to the gap between the vertical axis of the screen and the vertical axis of the actual space because humans feel gravitational acceleration with the vestibular organ. In view of this, there is a conventional technique which detects a tilt of a head portion by a sensor and rotates a rectangle display region such that the tilt is corrected, thereby causing a viewer to feel that the image to be displayed is fixed horizontally even when the head portion is tilted.
In recent years, HMDs have been reduced in size and weight, and more convenient glasses-type HMDs are increasingly proposed instead of large goggle-type HMDs. Unlike the goggle-type HMDs which provide immersive viewing that totally hides the actual neighboring environment from view, a viewer who uses the glasses-type HMD in which a see-through lens or a small diameter of lens is employed will also see the actual neighboring environment in addition to an image on the HMD display. This type is suitable for viewing mobile video image content. It is assumed to be used while moving on vehicles or while walking. When the lightweight glasses-type HMD is used in such a state where the head portion moves or shakes, there is a possibility that the positional relationship between the HMD and the head portion changes.
To address the problem of the gap between the position of a viewer's eye and a screen position, which occurs according to the state of mounting the HMD, Patent Literature (PTL) 2 discloses a technique for correcting a gap in a horizontal direction and a vertical direction according to a visual field of a viewer, and PTL 3 discloses a technique for correcting a gap in a horizontal direction and a vertical direction by obtaining a position of an eyeball from an image of an iris or a pupil.